A villager wrote to South Cambridgeshire District Council to complain about the smell from the sewage works and got a detailed reply which is reproduced below with their permission.

Thank you for your recent email concerning the above matter.

This Department has been made aware of the odour that has been emanating from the sewage treatment works and the problems that Anglia Water are experiencing in relation to the site.

The odour can be from a number of sources. After the heavy rain etc over the winter/ spring period odours were produced by the storm lagoons that were brought into action and then drained. When they drain, sludge deposits in the lagoon and then breaks down naturally.

Recent operational problems were encountered with the filter beds that had become blocked and ponding of effluent had occurred on top of the beds. Remedial action was taken to free-up the filter medium to maintain the flow. Further investigations by Anglia Water have since taken place as to why these beds were allowed to become blocked and attention was turned to the primary settlement tanks.

These primary settlement tanks accept raw sewage and the solids are allowed drop to the bottom. Scrappers move these solids to the centre of the tank, where they are removed to the new treatment plant. The site operates at maximum capacity over the winter period and draining of the settlement tanks is not possible. One of the tanks has now been taken offline and drained revealing that these scrappers have been severely damaged and are in need of replacement. This is a considerable job and will require the all of the tanks to be systematically drained and the necessary work carried out to each.

The current odour problems have occurred because sludge is settling in the bottom of the tanks and is not being cleared away. It is turning septic, resulting in sludge deposits bubbling to the surface and then incorrectly being carried to the filter beds, instead of the sludge treatment plant as intended.

I can confirm I have visited the site and the management have been very willing to comply with our requests and are attempting to rectify the situation as quickly as possible. However, due to company purchasing policy, delays have occurred in contractors submitting quotes etc and arranging for the works to be commenced. It is anticipated that quotes will be submitted in the very near future and works can then be started.

I appreciate that the smell is bad and has been around the area for sometime now. But Anglia Water have carried out their own investigations, emergency repairs and are now taking steps to rectify the problems that have been discovered. They also recognise the need for an ongoing preventative maintenance programme, which will identify such faults before they occur, as the site is going to remain at this location.

Unfortunately, as you are probably be aware it is not possible to take this works out of action until the problem is resolved.

I hope the above gives some reassurance that the matter has/is being looked into and a solution to the current problems is now hopefully in sight and this Department will be watching future developments with interest.

If you have any queries or wish to discuss this matter further please do not hesitate to contact me.

Yours sincerely
Nick Atkins
Environmental Health Officer
South Cambridgeshire District Council

As you can see it includes yet another explanation for the smell from Anglian Water, but one that has a ring of truth about it. The problem now is that looks like it will take some time to fix properly.